Summary of Research
Photomechanical motion of aromatic diimide molecules
Materials that are capable of change their shape and size, or of actuation by physical stimuli are ofparticular importance as media for conversion energy to mechanical work. Such mechanically
responsive or actuating materials are promising candidates as dynamically active elements providing awide range of applications: e.g., artificial muscles, actuators, and electromechanical devices. Thesemechanical responses are based on local chemical changes triggered by molecular motions, whichtransferred to distortion of macroscopic shape of bulk material. When physical stimulus isphoto-irradiation, mechanical response materials are classified into three mechanisms. One is cis-transisomerization, the others are ring opening and closure reactions, and cycloaddition reactions.
We recently found the photochemical reaction of naphthalene diimides having alkylamino side
chains in the solid states. Upon irradiation of light (λ = 370 nm), the compound of 1 showed color
change from yellow to black (Fig.1ab). After standing in dark, the color of 1 recovered to be yellow.
This came from the formation of radical anion of 1 as evidenced by UV-Vis-Nir spectroscopy.
Furthermore, the crystal 1 showed photomechanical motion (Fig.1c). Based on the magnetic
susceptibility and the theoretical calculation, the mechanical motion of 1 was accounted for electronic•‒•‒‒
repulsions among 1-1 , (1)2 , and 1-1 . a)
OOb)
NTherefore our observed photomechanicalhν
darkNN
Nairmotion was found to be a novelOO1c)
OO
mechanism based on the radical formation
NNNby photo-irradiation. Currently we arehν
darkNOOtrying to develop to a practical application
air1·−
for photo-actuator as an environmental
Fig.1 a)�Chemical structure of 1 and 1·−�b) Color change of 1 upon
irradiation �λ=370nm�c) Mechanical motion of 1�
device.
Molecular recognition by nanoscaled macrocyclic moleculesA) Nanotube as chemo-sensor
Pyromellitic diimide is known to be an electron acceptor. We synthesized various kinds ofnanoscaled macrocyle consiting of pyromellitic diimide (PDI). Because of the electron-poor cavity,
these macrocycles act as the host for the electron-donor molecules, which are recognized by the chargetransfer (CT) interaction. The most revealing property is that 2 formed gel by complexation withN,N-dimethylaniline. After treatment from gel to xerogel, the resulting structure was found to be theMeO
formation of nanoscaled porous tubegela)b)
OO NOMeN(Fig.2ab). This porous nanotube have aOO
2function as chemo-sensor: the nanotube 2O
OC H N(Me)NN OxerogelO
showed color change from pale yellow toMeOOMedrying inOO
vacuoOMepurple red by changing guest adsorbates.
MeONNOO
2
With increasing of the donor ability of thec)guest molecule, the absorption bond wasshifted to red due to increasing CTNoneinteraction (Fig.2c). Thus, our observed
Fig.2 a) Macrocycle containing of PDI�2�b) Gelation induced by themolecular sensing based on the CT complex with C H N(Me) , and formation of nanoscaled porous tube
6 5
2interaction considerably reflects the guest c) Color change of tubular 2 by adsorption of guest�
property.
6MeNMeHNMe52HNHMeOOMe

Et3PNEt3P Pt PEt3

Pt

PEt3

Et3P
PtPEt3NNN

NN NNEt3PNNN

PEt3
Pt
PEt3

Pt

PEt3

PEt3
Pt
Et3PNNNN△ 1-BuOH○ 2-BuOH■ iso-BuOH

3 -1

NAdsorbed / cm g S.T.P.

B) A giant macrocycle
The condensation reaction of aldehyde with cyclic urea and/or with amine spontaneously proceeds,
and then gives thermodynamically stable product. By changing the reaction condition such as acidityof media or use of rigid substrate, we can choose the size and the number of the units of thecomponent of the macrocycle at will. The condensation reaction of formalin with ethylene urea gave
6-membered macrocycle at 6N HCl condition, while a large 12-membered ring was obtained at weakacidic condition. On the other hands, the reaction between the rigid di-aldehyde and the tri-amine gavea giant tetrahedral macrocycle 3 (Fig.3a). Noteworthy is the fact that the size of 3 is 23 Å. This
macrocycle 3 was found to have thea)
b)
c) 35
30
property to increase in volume in solution
25
by complexation with guest solvent
2015
molecules. In the crystalline state, 3 formed
10mesoporous structure (Fig.3b).
The
50lipophilic pores of 3 uniformly formed in an00.20.4
0.60.813p/p
ordered array, and contribute to the Fig.3 a) Giant macrocycle 3 b) A uniformly ordered array of
lipophilic mesopores of 3 c) BuOH isotherm of 3. Selectivity of 1selective adsorption of 1-BuOH among the BuOH as high as 4.3 among the isomers at p/p0=0.3.�
isomers of butanol (Fig.3c).
0Molecular assembly: Exciton interaction in small π-electronic molecular aggregate
A simple streptopolymethine merocyanine is composed of electron donating nitrogen and electron
accepting oxygen, linked by a conjugated odd number of methine carbons. Due to the asymmetricalstructure, merocyanines are peculiar in their optical and photophysical properties. Although theoreticalstudies of a streptopolymethine merocyanine predict that exciton interaction is present among its
aggregates, very little experimental evidence has been reported so far. We have addressed this issue by
using 4-amino-6-oxopyrimidine derivatives. Since the parent 4a contains the simple merocyanine
structure in the molcular skelton with several hydrogen bonding sites, self-association of 4a forms anordered aggregate structure (Fig.4a). The absorption and fluorescence spectral properties of 4a clearly
showed that the molecule 4a formed the aggregate, and showed an exciton band, appearing at anabsorption of 350 nm due to the red-shifted HOMO‒LUMO transition. Upon light irradiation of theexciton band, a fluorescence band at 398 nm (ΦFL = 0.10) was observed. Based on these spectralfeatures, the aggregated 4a was fond to form J-type aggregation (Fig.4bc). Next, the simple isobutylgroup at the 4 position of the amino group can change the mode of the self-assembly of 4c from thelinear tape structure to the novel hexameric ball-like supramolecular structures by the interplay ofhydrophobic and H-bonding interactions (Fig.4d). The hexameric ball was found to be stable than thetape by comparison of solubility curves theRa) Rc) R
polymorphic crystal of 4c.
NNO HOHHNO HNNNNH
In the crystal of 4a and 4a·1.5H2O, 4aNNNHHNHOHONNNNformed supramolecular structure as an infinite
HRR
4a: R1 = H
4b: R2 = Medouble H-bonded ribbon. Since the observed
4c: R3 = iBud)
molecular arrangements are rarely found in the b) RONliterature, IR spectral analysis and theoreticalHN HNR
O
calculation were studied, and revealed that theHN
N H
Ncooperativity of the hydrogen bonding ranged
Fig.4 Chemical structure of 4-amino-6-oxopyrimidines
up to 9-mer of 4a.
(a) and their supramolecular structures;b) linear tape c) π-π stacking d) hexameric bowl (4c)�